32 TECHNICAL BULLETIN 14 9, TJ. S. DEPT. OP AGRICULTUKE 

 RESULTS OF EXPERIMENTS WITH THE YEASTS 



In the experiments with yeasts, ordinary baker's yeast, certain iden- 

 tified yeasts isolated from bees, and several unidentified species, were 

 used. The specific identifications were determined by comparison of 

 the morphological and cultural characteristics of the yeast with those 

 given for these species by Guilliermond (13) . Introductions through 

 the alimentary canal were made by mixing cultures of yeast with the 

 food, by caging bees on the cultures, and by wetting them with water 

 suspensions of yeasts. Inoculations were made directly into the 

 blood of bees through wounds made with a sterile needle. The foods 

 with which the yeasts were mixed included dilute honey, 10 to 20 

 per cent sugar solution, and Laurent's medium for yeasts to which 

 about 20 per cent of sugar or honey was added. 



A dysenteric condition appeared among caged bees that were heav- 

 ily inoculated by feeding on SaocharonrmfGes elUpsmdeus Hansen, S. 

 cerevisiae Hansen, and on two cultures of Mycoderma oeremsiae 

 Desm. and Hansen that differed in cultural characteristics. Uninocu- 

 lated bees kept under conditions as nearly identical as could be ob- 

 tained were not similarly affected. No effects were noticeable from 

 feeding on Saccharomyces aficuLatus Klocker and one other unidenti- 

 fied, slow-growing yeast. The death rate among inoculated bees 

 averaged higher than among the checks for the entire series of ex- 

 jDeriments, although the difference was so small that its significance is 

 as yet uncertain. 



When bees were heavily inoculated by feeding on 8. cerevisiae and 

 /S. ellipsoideits, taken from cultures on potato slants, a condition re- 

 sembling intoxication developed. Gas, which gave positive tests 

 for CO2, was formed within the ventriculus of the intoxicated bees. 

 Recovery from this condition, however, occurred within three or 

 four hours, and the death rate among the bees remained normal when 

 the food containing yeast was replaced with pure honey. 



Caged bees were unaffected when small quantities of yeast were 

 mixed with their food, and bees in colonies were apparently un- 

 affected when the only food available consisted of dilute honey or 

 sugar sirup with which half a dozen yeast cultures were mixed. 



Limited growth was observed to occur within the ventriculus of 

 infected bees when their food consisted of dilute honey sirup or 

 Laurent's medium. Growth never progressed farther, however, 

 than the formation of one or two buds by less than 20 per cent of the 

 cells. In about 3 or 4 days after bees were given the cultures most 

 of the yeast had passed from the ventriculus into the rectum. Yeast 

 cells within the contents of the rectum were found to be viable up to 

 10 days after being eaten. 



When the inoculation with yeasts was made in the blood by punc- 

 tures in the thorax, infection and death resulted in from 50 to 100 

 per cent of the individuals. With Saccharomyces apiovZatvs death 

 resulted in about 50 per cent of the cases. Weakening and crawling 

 of some of the inoculated bees was first noticed after 2 days, and 

 death usually occurred in less than 24 hours after the first symptoms 

 were apparent. Most of the inoculated bees that were infected died 

 in from 214 to 6 days after they were inoculated. A few died of 

 disease after 8 days, although as a rule those that survived for 8 

 days after inoculation had not been infected. 



